Add comprehensive security audit (86 findings across 10 areas)

Secure dev auth with signed tokens, add email support for --user
Simplify breakpoint variables, suppress Sass deprecation warnings

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

package.json

@@ -39,7 +39,7 @@
         "postcss": "^8.1.14",
         "prettier": "^3.0.0",
         "resolve-url-loader": "^5.0.0",
-        "sass": "^1.87.0",
+        "sass": ">=1.87.0 <3.0.0",
         "sass-loader": "^12.6.0",
         "select2": "^4.1.0-rc.0"
     },